The present invention relates generally to the field of hollow cathode lamps and, more particularly, to an improved hollow cathode lamp which limits the deposition of flashed getter metals on the stem and cathode leads of the lamp.
A variety of designs are known for hollow cathode lamps. Hollow cathode lamps used in extreme conditions are often designed such that two cathode leads and two anode leads carry electrical energy from the power supply, through the glass stem of the lamp, to the cathode and anode inside the lamp. It is known that hollow cathode lamps which must operate for extended periods of time and from which a high-quality spectrum is required (i.e., spectra calibration lamps for satellite instruments) should include a getter to collect contaminant gases after the lamp is sealed. It is known that a getter can extend the service life of the lamp by assuring that the spectra of the lamp will not become contaminated with hydrogen, oxygen, or water vapor that diffuses from the internal components. The getter, composed of a reactive metal such as barium, is heated until the metal vaporizes, or flashes, inside the lamp, thereby trapping any foreign gases in a location where they cannot enter the spectra.
In the prior art, some of the vaporized or flashed getter metal will form a film on the cathode leads. This contact produces a negative potential in the getter film. As an unfortunate result, the electrical discharge of the lamp may occur between the anode and the getter film, rather than between the anode and the cathode. In effect, the getter film will operate as the cathode. Because it is necessary to have the cathode metal produce the emitted spectra, rather than the getter metal, a discharge between the anode and the getter-metal film renders the lamp useless. Hence, it would be useful to provide a hollow cathode lamp with a flash shield that limits the deposition of the getter metal on the cathode leads and stem so as to prevent the getter metal from obtaining a negative potential and, thereby interfering with the proper operation of the lamp.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides an improved hollow cathode lamp (15) having a stem (23), a cathode lead (18) which passes through the stem, and a getter (26). The improvement comprises a flash shield (28) positioned between the getter and the stem, whereby the flash shield will limit the deposit of getter metal on the stem when the getter flashes.
The flash shield may be a circular disk and composed of nickel. The flash shield may include an evacuation passage (46). The flash shield may also be capable of being heated to about 1000xc2x0 C. during flashing, whereby the flash shield may be heated so as to convectionally repel the getter metal when the getter flashes.
Accordingly, the general object of the present invention is to provide an improved hollow cathode lamp with a flash shield which limits the deposit of getter metal on the stem and cathode leads of the lamp when the getter flashes.
Another object is to provide an improved hollow cathode lamp with a flash shield which is capable of being heated so as to convectionally limit the deposit of getter metal on the stem when the getter flashes.
Another object is to provide an improved hollow cathode lamp with internal supports which provide stability to the internal components of the lamp.
Another object is to provide an improved hollow cathode lamp which prevents the getter metal from obtaining a negative potential.
Another object is to provide an improved hollow cathode lamp with a flash shield which allows for unrestricted evacuation of the bulb when sealing the lamp.
Another object is to provide an improved hollow cathode lamp with a flash shield which allows for high pumping speeds during evacuation.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims.